Semiconductor laser

Abstract

Provided is a semiconductor laser which has a low operating current and stably oscillates even for high-temperature output. The semiconductor laser is provided with a substrate ( 10 ); an n-type clad layer ( 12 ) arranged on the substrate ( 10 ); an active layer ( 13 ) arranged on the n-type clad layer ( 12 ); a p-type clad layer ( 14 ), which is arranged on the active layer ( 13 ) and composed of a compound containing Al and has a stripe-shaped ridge structure to be a current channel; a current block layer ( 16 ), which is arranged on the surface of the p-clad layer ( 14 ) excluding an upper surface of the ridge structure and composed of a compound containing Al and has an Al composition ratio not more than that of the p-type clad layer ( 14 ); and a light absorption layer ( 17 ), which is arranged on the current block layer ( 16 ) and absorbs light at the laser oscillation wavelength.

The invention claimed is: 
     
       1. A semiconductor laser, comprising:
 a substrate; 
 a first conduction-type cladding layer provided on the substrate; 
 an active layer provided on the first conduction-type cladding layer; 
 a second conduction-type cladding layer which is provided on the active layer and composed of a compound containing Al, the second conduction-type cladding layer including a stripe-shaped ridge structure serving as a current channel; 
 a current block layer which is provided on a surface of the second conduction-type cladding layer except an upper surface of the ridge structure and is composed of a compound containing Al, the current block layer having a composition ratio of Al not higher than that of the second conduction-type cladding layer, a difference in the composition ratio of Al between the current block layer and the second conductive cladding layer being not more than 5%; 
 a light absorption layer provided so as to be directly contacted on a surface of the current block layer that absorbs light at a laser oscillation wavelength, the light absorption layer composed of a material having a band gap larger than that of the p-type cladding layer in order to serve as a current block layer confining an injected current; and 
 a contact layer formed on respective upper surfaces of the current block layer, a band discontinuity reduction layer, and the light absorption layer, 
 wherein an entire space on both of side surface sides of the ridge structure of the second conduction-type cladding layer and immediately below the contact layer is filled with the light absorption layer, inserting the current blocking layer between the ridge structure and the light absorption layer, and 
 wherein a saturable absorption region formed in the active layer and also under the current block layer absorbs and releases the laser light generated at the active layer for self-pulsation, the saturable absorption region being different from the light absorption layer. 
 
     
     
       2. The semiconductor laser according to  claim 1 , wherein the active layer includes a multi-quantum well structure having 5 to 8 barrier-well layer pairs. 
     
     
       3. The semiconductor laser according to  claim 1 , wherein thickness of part of the second conductive cladding layer where the ridge structure is not provided is 200 to 500 nm, and thickness of the current block layer is 100 to 400 nm. 
     
     
       4. The semiconductor laser according to  claim 1 , wherein total thickness of the part of the second conductive cladding layer where the ridge structure is not provided and the current block layer is 400 to 800 nm. 
     
     
       5. The semiconductor laser according to  claim 1 , wherein width of a bottom of the ridge structure is 1.4 to 4.0 μm. 
     
     
       6. The semiconductor laser according to  claim 1 , wherein thickness of the active layer is 15 to 90 nm. 
     
     
       7. The semiconductor laser according to  claim 1 , wherein the length of the ridge structure in the stripe direction is 250 to 500 μm. 
     
     
       8. The semiconductor laser according to  claim 1  further comprising a contact layer formed on respective upper surfaces of the current block layer, the ridge structure, and the light absorption layer. 
     
     
       9. The semiconductor laser according to  claim 1 , wherein the the band discontinuity reduction layer is formed on the upper surface of the ridge structure.